1. Field of the Invention
The present invention relates to a split stream flow cell which is used in a UV detector for liquid chromatography and in which light for detecting the absorption of light is transmitted through a sample solution in the cell.
2. Description of the Prior Art
A method of reducing the measurement time in liquid chromatography is one in which the flow of an eluate is changed with the passage of time.
However, since the base line of the output from a UV detector is changed by the flow (referred to as "flow effect" hereinafter), the detected value is incorrect.
Therefore, a split stream flow cell has been proposed as a means for solving the above-described problem (U.S. Pat. No. 3,614,452). This split stream flow cell has an arrangement in which an inlet channel communicates with the center of a split flow channel passing through a cell block, an outlet channel communicates with both ends of the split flow channel, and openings at both ends of the split flow channel are closed by window members. Since the eluate from a column is passed through divided portions from the center of the split flow channel to the ends thereof, the influence of the flow upon the light transmitting through the cell is reduced, resulting in a reduction the extent to which the above-described base line changes.
Another method of reducing the measurement time is a gradient elution method in which the components of an eluate is changed with the passage of time.
However, if the components of the eluate is changed, since the known liquid lens effect causes light to be refracted and thus absorbed by the wall surface of the split flow channel, or the divergent light to be bent toward a photodetector element, the energy of light reaching the photodetector element is reduced or increased, with the base line of UV-detection thereby being changed.
A tapered cell is well known as a flow cell which reduces the liquid lens effect in openings at the ends of a tapered hole passing through a cell block (Japanese Patent Publication No. 33871/1979, U.S. Pat. Ser. No. 470,076). In order to reduce the liquid lens effect, it is necessary to increase the inclination of the inner wall of a cell with respect to the center thereof.
However, if the degree of inclination is large, the volume of the cell becomes too large, resulting in peak broadening or re-mixing of the components of a sample.
There is no flow cell in which the influences of the flow effect and the liquid lens effect are both reduced, and a proposal for such a flow cell has been awaited for a long time.